Various types of knocking or pinging prevention and control systems have been proposed--see the referenced patents and patent documents listed above. The systems, as proposed, control operation of the engine by adjusting the position of an operating control element thereof if an evaluation circuit, connected to a knock sensor, senses that the engine is operating under knocking conditions, or has a tendency to knock. Typical changes to prevent knocking of the engine are: changing the fuel-air ratio to provide a somewhat richer mixture, that is, one which has more fuel therein; providing additives to the fuel-air mixture to insure operation without knocking, by increasing the resistance to knocking of the engine. Typical additives are water, alcohols, aniline compounds, lead, or similar metallic compounds, as well as combinations thereof. Other changes which can be made are changes in the extent of exhaust gas recirculation (EGR), by controlling the gas being returned in a return loop; controlling the temperature of the air which is charged into the engine, for example by heating or cooling the intake air; controlling the temperature of the combustion mixture or the combustion components thereof, controlling the cooling of the engine, and, most importantly, controlling ignition timing and/or fuel injection timing in a fuel injected engine. An additional change suitable for turbocharged engines is to change the turbo charging pressure. Readily changed parameters are the introduction of additives, for example by injecting components which have a tendency to decrease knocking, and to control the charge pressure of induction air, for example the charge pressure of a turbocharger.
The various steps taken to decrease knocking can be carried out in dependence on actual sensing of knocking, and especially by counting the sequence and the number of knocking events, and the intensity thereof, which occur--see, for example, the referenced U.S. Pat. No. 4,153,020, King et al. Knock control systems are subject to the problem that, if the knocking is slight, or occurs only from time to time, the control loop may overreact. Such overreaction can be avoided by making the control loop operate slowly. Yet, slow operation of the control loop prevents rapid reaction to substantial knocking which suddenly occurs.